Many major lumbar spine operations require the use of pedicle screws. The pedicle linking the vertebral body to the lamina has some of the densest bone in the spine. Once screws have been placed in the pedicles of the involved vertebrae, the screws can be position along rods and tightened to lock the vertebrae into a fixed position. This is often done as part of a spinal fusion surgery. In this illustration, the space between L5 and S1 is being reopened. Moss Miami System - reprinted with permission of Depuy Spine, Inc.